Differentiating between adductor and abductor spasmodic dysphonia using airflow interruption

Objectives/Hypothesis: To measure the laryngeal resistance (RL), subglottal pressure (P_s), and mean flow rate (MFR) of adductor (ADSD) and abductor (ABSD) spasmodic dysphonia patients using the airflow interrupter.Methods: The RL of six ABSD and seven ADSD patients was measured using the airflow interrupter, a noninvasive device designed to measure MFR and P_s via mechanical balloon valve interruption. Subjects performed 10 trials at each of two intensity levels, with each trial consisting of a sustained /a/ during which phonation was interrupted for 500 ms. Laryngeal resistance was calculated as subglottal pressure divided by airflow.Results: Mean RL for the ADSD and ABSD subtypes at 65 dB were 24.78 cmH₂O/L/s and 14.51 cmH₂O/L/s, respectively (P = .04). Mean RL at 70 dB were 40.02 cmH₂O/L/s and 15.84 cmH₂O/L/s (P = .014). Ps for the ADSD and ABSD subtypes at 65 dB were 10.23 cmH₂O and 8.32 cmH ₂O, respectively (P = .582). At the 70 dB level, P_s were 12.39 cmH₂O and 11.78 cmH₂O (P = .886). MFR for the ADSD and ABSD subtypes at 65 dB were 435 mL/s and 746 mL/s (P = .205). Mean MFR at 70 dB were 518 mL/s and 848 mL/s (P = .198).Conclusions: Noninvasive measurements of RL may be useful for differentiating between ADSD and ABSD. This simple objective test, which produces a quantitative output, could be used to evaluate laryngeal function in patients with spasmodic dysphonia.